This invention relates to novel, environmentally stable segmented aliphatic polyurethanes and methods or processes of making same.
The chemistry of urethanes and polyurethanes is, of course, extensive and well developed. For some period of time, polyurethane materials, such as materials sold by Dow Chemical Co. under the trade designation Pellethane.RTM., have been used for implantable biomedical applications. Pellethane.RTM. 2363-80A and 2363-55D are widely used polyurethanes particularly for implantable cardiac pacing leads.
There also is an extensive polyurethane patent art. U.S. Pat. Nos. 4,191,818, 4,521,582, 4,098,773, among others, are representative of numerous examples of this art. U.S. Pat. No. 4,191,818 to Illers et al relates to polyurethane elastomers made by a process in which a polyisocyanate is reacted with a polyol of high molecular weight with an OH:NCO ratio of 1:0.66 to 1:0.85. The resulting prepolymer is further reacted with an excess of symmetrical diisocyanate and a diol chain extender.
U.S. Pat. No. 4,521,582 to Goyert et al relates to novel, thermoplastically processed branched polyurethane based on naphthylene-1,5-diisocyanate. The process of Goyert et al involves the reaction of a long chain polyester, polyether or polycarbonate polyol with sub-stoichiometric quatities of any diisocyanate other than naphthylene-1,5-diisocyanate. The resulting prepolymer then is further reacted with excess naphthylene-1,5-diisocyanate and with a chain lengthening mixture of short-chain diols and triols or polyols in specific ratios.
U.S. Pat. No. 4,098,773 also to Illers et al concerns a process for making heat resistant polyurethane elastomers in which a substantially linear poly-hydroxyl, polyether, polyester or polycarbonate compound is reacted with diisocyanate material in amounts to give an OH:NCO ratio of 1:1.10 to 1:2 and reacting the resulting adduct with symmetrical aromatic diisocyanate and a diol as chain extender.
Polyurethanes presently used for implantable applications include Biomer.RTM. segmented polyurethane, manufactured by Ethicon, Inc., of Sommerville, NJ, Cardiothane.TM. polyurethanes, sold by Kontron, Inc., Pellethane.RTM. polyurethanes, sold by Dow Chemical, and Tecoflex.TM. polyurethanes sold by Thermedics, Inc. These polyurethanes and others are described in the article "Biomedical Uses of Polyurethanes", by Coury et al, in Advances in Urethane Science and Technology, Vol. 9, edited by Kurt C. Frisch and Daniel Klempner, Technomic Publishing Co., Lancaster, PA, 1984, pp. 130-168. These pages are incorporated herein by reference in their entirety.